Gtk (GTK+) is a Graphics Toolkit written in C, primarily developed for use with the X Window System. GTK+ is licensed under the GNULGPL license and has bindings for many languages including Ada95, C++, Common Lisp
(see GTK bindings), Dylan, Eiffel, Guile, Haskell, JavaScript, Objective C, Objective Caml, Objective Label, Pascal, Perl, Pike, Python, and TOM. It's a major component of the GNOME project.